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| 型号： | AD8557ARZ-REEL7 |
| 厂商： | Analog Devices Inc |
| 文件页数： | 8/24页 |
| 文件大小： | 0K |
| 描述： | IC AMP CHOPPER 2MHZ 55MA 8SOIC |
| 标准包装： | 1,000 |
| 系列： | DigiTrim® |
| 放大器类型： | 断路器（零漂移） |
| 电路数： | 1 |
| 增益带宽积： | 2MHz |
| 电流 - 输入偏压： | 18nA |
| 电压 - 输入偏移： | 2µV |
| 电流 - 电源： | 1.8mA |
| 电流 - 输出 / 通道： | 55mA |
| 电压 - 电源，单路/双路(±)： | 2.7 V ~ 5.5 V |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 供应商设备封装： | 8-SO |
| 包装： | 带卷 (TR) |
AD8557
Rev. C | Page 16 of 24
OPEN WIRE FAULT DETECTION
The inputs to A1 and A2, VNEG and VPOS, each have a com-
parator to detect whether VNEG or VPOS exceeds a threshold
voltage, nominally VDD 1.1 V. If VNEG > (VDD 1.1 V) or
VPOS > (VDD 1.1 V), VOUT is clamped to VSS. The output
current limit circuit is disabled in this mode, but the maximum
sink current is approximately 10 mA when VDD = 5 V. The
inputs to A1 and A2, VNEG and VPOS, are also pulled up to
VDD by currents IP1 and IP2. These are both nominally 16 nA
and matched to within 3 nA. If the inputs to A1 or A2 are
accidentally left floating, as with an open wire fault, IP1 and IP2
pull them to VDD, which would cause VOUT to swing to VSS,
allowing this fault to be detected. It is not possible to disable IP1
and IP2, nor the clamping of VOUT to VSS, when VNEG or
VPOS approaches VDD.
SHORTED WIRE FAULT DETECTION
The AD8557 provides fault detection in the case where VPOS,
VNEG, or VCLAMP shorts to VDD and VSS. Figure 46 shows
the voltage regions at VPOS, VNEG, and VCLAMP that trigger
an error condition. When an error condition occurs, the VOUT
pin is shorted to VSS. Table 8 lists the voltage levels shown in
VPOS
VNEG
VSS
VINL
VINH
VDD
VSS
VCLL
VDD
VCLAMP
VSS
VINL
VINH
VDD
ERROR
NORMAL
ERROR
NORMAL
ERROR
NORMAL
06013-
039
Figure 46. Voltage Regions at VPOS, VNEG, and VCLAMP
that Trigger a Fault Condition
Table 8. Typical VINL, VINH, and VCLL Values
(VDD = 5 V)
Voltage
Min (V)
Max (V)
VOUT Condition
VINH
3.9
4.2
Short to VDD fault detection
VINL
0.195
0.55
Short to VSS fault detection
VCLL
1.0
1.2
Short to VSS fault detection
FLOATING VPOS, VNEG, OR VCLAMP FAULT
DETECTION
A floating fault condition at the VPOS, VNEG, or VCLAMP
pins is detected by using a low current to pull a floating input
into an error voltage range, defined in the previous section. In
this way, the VOUT pin is shorted to VSS when a floating input
is detected. Table 9 lists the currents used.
Table 9. Floating Fault Detection at VPOS, VNEG,
and VCLAMP
Pin
Typical Current
Goal of Current
VPOS
16 nA pull-up
Pull VPOS above VINH
VNEG
16 nA pull-up
Pull VNEG above VINH
VCLAMP
0.2 A pull-down
Pull VCLAMP below VCLL
DEVICE PROGRAMMING
Digital Interface
The digital interface allows the first stage gain, second stage
gain, and output offset to be adjusted and allows desired values
for these parameters to be permanently stored by selectively
blowing polysilicon fuses. To minimize pin count and board
space, a single-wire digital interface is used. The digital input
pin, DIGIN, has hysteresis to minimize the possibility of
inadvertent triggering with slow signals. It also has a pull-down
current sink to allow it to be left floating when programming is
not being performed. The pull-down ensures inactive status of
the digital input by forcing a dc low voltage on DIGIN.
A short pulse at DIGIN from low to high and back to low again,
such as between 50 ns and 10 s long, loads a 0 into a shift
register. A long pulse at DIGIN, such as 50 s or longer, loads a
1 into the shift register. The time between pulses should be at
least 10 s. Assuming VSS = 0 V, voltages at DIGIN between
VSS and 0.2 × VDD are recognized as a low, and voltages at
DIGIN between 0.8 × VDD and VDD are recognized as a high.
A timing diagram example, Figure 47, shows the waveform for
entering Code 010011 into the shift register.
CODE
0
1
0
1
WAVEFORM
tW0
tWS
tW0
tWS
tW0
tWS
tW1
06013-
040
Figure 47. Timing Diagram for Code 010011
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